CEBAF Guns July 1999 - Present

Present JLab “Vent/Bake” Polarized Electron Gun

Cathode(GaAs)

NF3

Laser

Cs

Anode

e -

-100 kV

4 days to load, bake, prepare

new photocathode

(leaky)

(F.E.)

New Load Lock Gun Assembled & Running Spring ‘06

Suitcase

Small bake Load region

NEG-coated HV chamber

Heat/activation chamberGoal: 8 hours swap photocathodePresent: ~12 hours

x4

Load lock port(GaAs on puck)

NEG pipe

Laser(1 W @ 532 nm)

& attenuators

Faraday Cup(450 C bake)

High Voltage(-100 kV)

Activation(Cs/NF3,

Mask=5 mm)

Experimental Setup

350 m 1500 m

Spot SizeAdjustment

7 PrecisionIon PumpSupplies

SolenoidCentering

Benchmarking the NEW Load Lock Gun (2006-2007)

13 mA!

CEBAF ~2500 C/year

LL Gun ~ 2500 C/week• No RF structure• Low-P wavelength

Demonstrated world bestGaAs lifetimes, & up to 10 mA

Qweak to test standard model >200 A at 85% polarization

Proposed e-/ion collider facilitiesJLab ELIC (>1 mA), BNL eRHIC (>50 mA)

Future: High Current & High Polarization Programs

~20 C/day Circulator <1 C/dayLinac >100 C/day

Ingredients: Good gun, good photocathode, powerful laser

100

nm

Superlattice GaAs: Layers of GaAs on

GaAsP

No strain relaxationQE ~ 1%

Pol ~ 85%@ 780 nm

chekc14 pairs

Fiber-based LaserNEW Load Lock Gun

Now: High Current & High Polarization

Friday, Saturday & Sunday

Brief opportunity to use one of the fiber lasers, before installed into CEBAF on Monday:

•Superlattice high-P material (85%)•Very good QE ~1% in New Gun•First running with 499 MHz RF

Qweak Demonstrated250 A (2 days, 70 C)Lifetime 250-1000 C(translates > 1 week running/spot)

ELIC Circulator Ring Demonstrated1 mA (10 hr, 30 C)Lifetime ~200 C